1. Field of the Invention
The present invention relates to a fluid sensor that actuates in a fluid, and more particularly to a fluid sensor that actuates in a corrosive fluid such as sulfuric acid, particularly in a lead storage battery or in a polar solvent tank.
2. Description of Related Art
A sensor device having a piezoelectric element or the like is used for the measurement of the viscosity of a fluid, the detection of solid particles in a fluid, the detection of vibrations, etc. For example, in the sensor device disclosed in U.S. patent application Ser. No. 08/560,658, a piezoelectric film and a vibrating portion are vibrated, and the viscosity of a fluid is measured in accordance with a change in the loss coefficient, the electric resistance, the reactance or the like of the piezoelectric film. In this example, since the piezoelectric film or the vibrating portion is in contact with the fluid, when the viscosity of the fluid is large, the vibration of the piezoelectric film and the vibrating portion become small in amplitude. On the other hand, when the viscosity of the fluid is small, the vibration of the piezoelectric film and the vibrating portion become large in amplitude. Then, when a voltage is applied to the piezoelectric film, a current corresponding to the amplitude is detected. In the case where the viscosity of the fluid correlates with the concentration of the fluid or the density of components in the fluid, the concentration or the density of the fluid can be also detected. For example, a sulfuric acid aqueous solution has a given correlation between the viscosity and the concentration, as well as a given correlation between the viscosity and the density of sulfuric acid.
Also, the detection of solid particles in the fluid is proposed in U.S. patent application Ser. No. 08/443,464 that discloses a particle sensor having a piezoelectric film. With the collision of particles in the fluid with a detecting portion having the piezoelectric film or a vibrating portion to which the detecting portion is fixed, the vibrating portion and the detecting portion vibrate, the piezoelectric film converts the vibrations into an electric signal, and a pair of electrodes between which the piezoelectric film is interposed outputs that electric signal.
In the case of measuring the viscosity of the fluid, detecting the solid particles in the fluid, and detecting the vibrations by use of the above-structured sensor device, there is required that the sensor device is disposed in the fluid with the result that an electrode terminal for extracting a signal from the sensor device that actuates in the fluid to the exterior must be held gas-tightly and/or liquid-tightly with respect to the fluid.
For the above reason, up to now, as shown in FIG. 5, a lead wire 11 is connected to an electrode terminal 6, and its connected portion is then molded with an organic resin 30 or the like so as to be sealed such that the electrode terminal is held gas-tightly and/or liquid-tightly with respect to the fluid.
However, in the above conventional method, because an adhesion of the organic resin to a ceramic material of which a base body of the sensor device is made is weak, there arises such a problem that the molding organic resin 30 or the like is caused to be readily separated from the connected portion.